Chapter 18 Virtual Circuit Switching Frame Relay and

Chapter 18 Virtual Circuit Switching : Frame Relay and ATM Kyung Hee University 1

18. 1 Virtual Circuit Switching Global Addressing Virtual Circuit Identifier Three Phases Data Transfer Phase Setup Phase Teardown Phase Kyung Hee University 2

Virtual circuit wide area network Kyung Hee University 3

Global Addressing q In virtual circuit networks, global addressing is used only to create a virtual circuit identifier. Kyung Hee University 4

Virtual Circuit Identifier (VCI) q Each switch can use its own unique set of VCIs Kyung Hee University 5

Three Phases Kyung Hee University 6

Three Phases q In the setup phase, the source and destination use their global addresses to help switches make table entries for the connection. q In the teardown phase, the source and destination inform the switches to erase the corresponding entry. q Data phase occurs between these two phases. Kyung Hee University 7

Data Transfer Phase q To transfer a frame from a source to its destination, all switches need to have a table entry for this virtual circuit. Kyung Hee University 8

Data Transfer Phase (cont’d) q Source-to-destination data Transfer Kyung Hee University 9

Setup Phase q How does a switch create an entry for a virtual circuit? v Permanent virtual circuit (PVC) approach v Switched virtual circuit (SVC) approach Kyung Hee University 10

Permanent Virtual Circuit (PVC) q Simple way q Like a leased line q The corresponding table entry is recorded for all switches by the administrator (of course remotely and electrically) q In the duplex communication, two virtual circuit are established. Kyung Hee University 11

Switched Virtual Circuit (SVC) q Creating temporary and short connection that exists only when data are being transferred between source and destination. q Setup request VCI (77) lets the destination know that the frames come from A and not other sources Kyung Hee University 12

SVC (cont’d) q SVC setup acknowledgment Kyung Hee University 13

Teardown Phase q In this phase, source A, after sending all frames to B, sends a special frame called a teardown request. q Destination B responds with a teardown confirmation frame. q All switches erase the corresponding entry from their tables. Kyung Hee University 14

X. 25 vs. Frame Relay Feature X. 25 Connection establishment At the network layer Hop-by-hop flow control and error control End-to-end flow control and error control Data rate Frame Relay None At the data link layer None At the network layer None Fixed Bursty Multiplxing At the network layer At the data link layer Congestion control Not necessary Necessary Kyung Hee University 15

X. 25 vs. Frame Relay Kyung Hee University 16

Features of Frame Relay q Operating in higher speed such as 1. 544 Mbps, 45 Mbps q Operating in just the physical and data link layers q Allowing bursty data q Allowing a frame size of 9000 bytes, which can accommodate all local area network fame sizes q less expensive q Error detection at the data link layer only v no flow control or error control Kyung Hee University 17

Architecture Kyung Hee University 18

Virtual Circuit q A virtual circuit in FR is identified by a number called a data link connection identifier (DLCI) q Using PVC and SVC Kyung Hee University 19

Virtual Circuit q SVC v SVC 연결에 필요한 DLCI Kyung Hee University 20

FR Switch q교환기 (Switch) v프레임 경로를 지정해주는 Table 이용 Kyung Hee University 21

FR Layers q Frame Relay operates only at the physical and data link layers q Frame Relay does not provide flow or error control; they must be provided by the upper-layer protocols. Kyung Hee University 22

Frame Relay frame EA 0 : meaning that another address byte is to follow DE 1 : not to discard this frame Kyung Hee University 23

Frame Relay frame Kyung Hee University 24

Congestion Control q 혼잡 회피(Congestion avoidance) v혼잡이 일어났음을 발신지와 목적지에게 알리기 위해 2개의 비트 사 용 q BECN(Backward Explicit Congestion Notification) v트래픽 혼잡이 일어났다는 것을 송신자에게 경고하는데 사용 Kyung Hee University 25

Congestion Control q. FECN(Forward Explicit Congestion Notification) v트래픽 혼잡이 일어났다는 것을 수신자에게 경고하는데 사용 Kyung Hee University 26

Congestion Control q 4 cases of congestion Kyung Hee University 27

FRAD Kyung Hee University 28

ATM q Asynchronous Transfer Mode (ATM) is the cell relay protocol by the ATM Forum and adopted by the ITU-T Kyung Hee University 29

Multiplexing using different frame sizes Kyung Hee University 31

Cell Networks q A cell network uses the cell as the basic unit of data exchange. A cell is defined as a small, fixed-sized block of information. Kyung Hee University 32

Multiplexing Using Cells Kyung Hee University 33

Asynchronous TDM Kyung Hee University 34

Architecture of ATM Network Kyung Hee University 35

Virtual Connection Kyung Hee University 36

Example of VPs and VCs Note that a virtual connection is defined by a pair of numbers: the VPI and the VCI. Kyung Hee University 37

Connection Identifiers Kyung Hee University 38

Virtual connection identifiers in UNIs and NNIs Kyung Hee University 39

An ATM Cell Kyung Hee University 40

Routing with a Switch Kyung Hee University 41

ATM Layers Kyung Hee University 42

ATM layers in endpoint devices and switches Kyung Hee University 43

ATM Layer Kyung Hee University 44

ATM Headers Kyung Hee University 45

Questions ! Kyung Hee University 50